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Re: [Asrg] Unique innovations made to anti-spam system

2006-01-23 10:32:17
On 2006-01-22 20:22:33 +0000, Michael McConnell wrote:
On 22nd January 2006 at 21:07, Peter J. Holzer wrote:
On 2006-01-22 19:40:09 -0000, John Levine wrote:
Russ Nelson has experimented with a R (no C) technique based on this
observation.  When a message from an unfamiliar address arrives, his
setup sends an auto-ack and puts the mail into a holding pen.  If the
auto-ack bounces, he moves the message into the spam folder.  If after
15 minutes or so there's no bounce, the message moves into the inbox.

He said it works quite well.

However, it still sends mails to innocent bystanders. It is mitigated by
the fact that each address only gets one mail, but if this is widely
implemented, the owners of the forged sender addresses used by spammers
will be bombarded with auto-ack messages.

That would depend if the auto-ack is an entire message, DATA and all, or 
whether it stops after checking the response code to RCPT TO at the sender's 
mailserver.

That's a different technique, which is already implemented in some
standard MTAs. Postfix calls this "sender verification", Exim uses the
more descriptive term "smtp callback". The problem with this approach is
that a positive reply to a RCPT TO is no guarantee that the address
exists. Some sites accept all mails and then send bounces. Russ' Scheme
gets around this problem but at the cost of potentially being much more
annoying to forgery victims. (I guess that it could be combined with SPF
or DKIM to give victims an easy way to avoid being ddossed)

        hp

-- 
   _  | Peter J. Holzer    | Ich sehe nun ein, dass Computer wenig
|_|_) | Sysadmin WSR       | geeignet sind, um sich was zu merken.
| |   | hjp(_at_)hjp(_dot_)at         |
__/   | http://www.hjp.at/ |    -- Holger Lembke in dan-am

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